The present invention relates to drilling apparatus and more particularly to a fast descent core barrel head assembly with mechanism to maintain the latches in a retracted position until the head assembly seats on the drill sting landing shoulder.
In many prior art wire line core barrel assemblies, the latch mechanism is mounted to the latch body and is forced out and held in a locked (latch seated) position by gravity or spring mechanism. With latch mechanism constantly resiliently urged transversely outwardly, the rate of descent in the drill string is slowed as a result of the latches dragging against the inner peripheral wall of the drill string.
It is a common occurrence in certain rock formations that the bore hole is completely dry to the bottom. One reason, as drilling fluid is pumped into the drill string and passes through the drill string, no fluid is returned to the surface in the annular space between the outer peripheral surface of the drill string and the surface of the bore hole as a result of fractured or porous rock formation wherein all the drilling fluid is absorbed or leaks into the formation rather than being pumped back to the surface. This problem is aggravated by increasing hole depths where the hydrostatic head pressure of the fluid column inside the drill string is greater than the pressure needed to flow fluid across the face of the drill bit. The result of this pressure difference is the condition in which, due to the fluid column head pressure, fluid is flowing through the drill bit at a faster rate than is being supplied into the drill string by the fluid pumped, a column of air develops inside the drill string. Due to the compressibility of air, the fluid flow across the bit face can stop under certain conditions and no significant increase in fluid gage pressure is denoted on the surface until after failure of the drill bit due to a lack of fluid flow across the bit face.
U.S. Pat. No. 3,120,283 to Braun discloses a core barrel inner tube assembly having an overshot coupling portion retained in a position by the latches in their retracted position to prevent fluid bypass until the latches move to their latch seated position and thence under gravity, or inward fluid pressure, move to permit fluid bypass and prevent the latches moving to their retracted position until the coupling portion is retracted.
U.S. Pat. No. 3,266,835 to Hall discloses a core barrel inner tube assembly fluidly propellable in any direction and includes a valve assembly connected to a spearhead and resiliently urged to a position to block fluid flow. When the inner tube assembly moves to its inner position, water pressure forces the spearhead assembly to move to open a bypass channel and allow the latches to move to a latch seated position. If the latches do not seat properly, a valve does not open and bypass is blocked.
U.S. Pat. No. 5,339,915 to Laporte et al discloses a one way retention valve in a core barrel inner tube assembly that functions to retain drilling liquid pressure in lost circulation situations resulting from, for example drilling into a cavity or into a broken earth formation. However, with such apparatus, the descent in a drill sting is very slow since the fluid bypass channel is blocked and liquid can not bypass except around the exterior of the latch body landing shoulder. Further, a heavy duty spring is used to create a high liquid pressure and retain a column of liquid above the core barrel inner tube assembly. This high pressure in combination with pump surging has resulted in wear on the valve ball seat. The ball essentially hammers the seat which, over a period of time, damages the seat.
U.S. Pat. No. 5,020,612 to Williams discloses a core barrel inner tube assembly having a resilient ring (bushing) in the fluid bypass channel through which a valve ball is forced by fluid under pressure when the inner tube assembly is in its core collecting position at the bit end of the drill string.
In order to make improvements in core barrel inner tube apparatus to enhance its rate of descent while maintaining a minimum head of fluid in the drill string during the drilling operation together with requiring the latches to be properly seated for the fluid retention system to function properly, and having a way of releasing the head of drilling fluid at the end of the drilling cycle prior to retraction of the apparatus off the drill string landing shoulder, this invention has been made.